Field of the Invention
This invention relates to an apparatus for wetting a web of material with a liquid. The material web is guided in a travel direction through the apparatus which includes a guide or guide means for guiding the material web and an applicator or application means for applying the liquid to the material web.
Discussion of Related Art
It is known for material webs such as a film, a nonwoven fabric, a paper, or a textile knit to be treated with generally liquid chemicals in order to provide the material web with a functional finish. This can, for example, be a coloring, an impregnation, a stain protection coating, a nanocoating, an antibacterial coating, or the like.
Such a method and a corresponding apparatus are known, for example, from German Patent Reference DE 10 2006 038 339 A1. In this case, the material web to be wetted is guided around a rotating application roller that is partially immersed in a chemical trough and applies the chemical from the trough to the material web. Two guide rollers that are respectively situated before and after the application roller guide the material web around the application roller.
One disadvantage of the apparatuses known from the prior art is that depending on the contact angle between the material web and the application roller, the material web speed, the material web grammage, the application roller speed, and the viscosity of the wetting substance, a permeation of the material web by the substance can occur at the apex of the application roller. Depending on the above-mentioned parameters, the degree of permeation can be so great that significant quantities of the wetting liquid emerge from the side of the material web oriented away from the application roller and are catapulted into the surroundings in a travel direction of the material web, thus producing an aerosol mist.
This aerosol mist is disadvantageous in many respects. It is deposited on surrounding surfaces of the equipment as a result of which these surfaces can become soiled and, depending on the chemical, can experience significant corrosion. Such a contamination of the equipment can reduce equipment safety. Buildup on floors and stairs results in slippery surfaces that form a risk of injury to personnel working on the apparatus. Under some circumstances, personnel are also exposed to harmful contamination of the breathable air by the aerosol mist. Liquid that is deposited on surrounding parts of the equipment, in particular crossbeams extending across the material web, can drip back onto the material web and thus negatively impact product quality. The aerosol mist escaping into the surroundings can result in a significant cost increase because up to 30% of the substance to be applied can pass through the material web and volatilize and thus cannot be used for the wetting.
Up to now, extraction hoods above the material web in the vicinity of the wetting have been used to extract the aerosol mist, but they represent a significant equipment expenditure and they can only be installed at a certain structurally required distance from the material web. For this reason, such devices cannot prevent liquid in the immediate vicinity of the wetted material web from volatilizing and/or becoming deposited on machine parts. The liquid that is deposited in the edge regions of the extraction hood can once again drip back onto the material web. Also, the extracted liquid generally can no longer be used for wetting and thus the loss of such liquid remains as insignificant as before.